The first major settlement on the site of what is today London was founded by the Romans in AD 43, following the Roman invasion of Britain. This settlement was called Londinium, commonly believed to be the origin of the present-day name, although a Celtic origin is also possible. This first London lasted for just seventeen years. Around AD 61, the Iceni tribe of Celts led by Queen Boudica stormed London, burning it to the ground. The next, heavily-planned incarnation of the city prospered and superseded Colchester as the capital of the Roman province of Britannia in AD 100. At its height in the 2nd century AD, Roman London had a population of around 60,000. However, by the 3rd century AD, the city started a slow decline due to trouble in the Roman Empire, and by the 5th century AD, it was largely abandoned.

Today, London is the most populous city in the European Union with an official population of 7.7 million (as of 2007) Its population is very cosmopolitan, drawing from a wide range of peoples, cultures and religions, speaking over 300 different languages. London is an international transport hub, with five international airports and a large port. It serves as the largest aviation hub in the world and its main airport, the multi terminal Heathrow, carries more international passengers than any other airport in the world.